On account of a continuing effort towards improving efficiency of steam turbine installations, it can be desirable to operate turbines at high temperatures. However known materials can exhibit poor performance above 650° C. and most particularly above 700° C. For this reason, turbine parts such as rotors, casings and blades can be made of more expensive exotic alloys. An example of one such alloy is described in U.S. Patent Application 2004/0253102 A1. While for cost reasons it may be beneficial to manufacture any component, as least partly, from known materials, it can be particularly desireable to do so for large components, like rotors, and for complex components, like blades.
A solution is to minimize exposure of component parts to high temperature. U.S. Patent Application US2007/0207032 A1, for example, describes one arrangement that provides a large temperature drop across the first stage and so only the first stage and any rotor components upstream of this stage are exposed to high temperature.
Another solution is to provide cooling medium to high temperature regions. It can however be technically difficult to provide enough cooling to large turbine components such as the rotor.